The space age began on the chill evening of October 4, 1957. Sputnik, a 184-pound (83 kilograms) aluminum sphere tucked into the nose of a Soviet R-7 ballistic missile, streaked skyward from its launchpad near the edge of the Kyzyl Kum desert about a hundred miles (170 kilometers) east of the Aral Sea to become the first man-made object to orbit the Earth. An epoch of exploration and discovery as momentous as any in history had begun. Humans would go on to orbit the Earth, float in space, and—most spectacularly—set foot on the moon.

Just 15 years later it was over—after the last Apollo mission to the moon in December 1972. The space shuttle, a technological marvel at its debut in 1981, has proved to be fragile, expensive, and dangerous. And since it cannot fly beyond low Earth orbit, it has transformed spaceflight into a series of high-tech cruises to nowhere. When Columbia disintegrated over Texas during reentry in 2003, killing all seven of its astronauts, investigators decried the aimlessness of the human spaceflight program.

In response, President George W. Bush has outlined a new “Vision for Space Exploration”: to return American astronauts to the moon by 2020 and eventually send them to Mars. The United States is ordering new rockets, building a new spaceship, making plans for a moon base—and, against long odds, trying to recapture the sense of urgency and adventure that propelled our first push into space.

The R-7 rocket that launched Sputnik was a technological tour de force and a tremendous challenge to the West. Not only had Soviet scientists, led by legendary rocket designer Sergei Korolev, developed a rocket capable of flinging nuclear weapons to U.S. soil, they had opened the path to the moon and beyond. “The present generation will witness how the freed and conscious labor of the people of the new socialist society turns even the most daring of mankind's dreams into reality,” declared a Soviet press release.

A month later the Soviets launched 1,120-pound (508 kilograms) Sputnik 2, six times heavier than its predecessor, with a dog named Laika aboard. Laika lasted only a few hours in the overheated spacecraft, but the Russians had made their point: If they could put a dog in orbit, they could send a human. Wernher von Braun, the transplanted Nazi scientist who would build the Saturn V rocket that launched the Apollo moon missions, begged Neil McElroy, the incoming secretary of defense: “For God’s sake turn us loose.”

Over the next few years, both the U.S. and the Soviet Union developed distinctive technologies, but they faced the same basic challenges. The physics of launch were, and are, immutable. An object flung into space has to reach a speed of between 17,000 and 18,000 miles an hour (27,000 and 28,000 kilometers) to attain low Earth orbit. To escape Earth’s gravity altogether and fly somewhere else, a spacecraft must travel 25,000 miles an hour (40,000 kilometers). The heavier the payload, the more powerful the rocket must be, and in this the Soviets initially had a huge advantage with the R-7. Four months after Sputnik, the U.S. did manage to orbit its first satellite, 31-pound (14 kilograms) Explorer 1—but by the end of the year the Soviets had launched Sputnik 3, weighing in at a ton and a half (1.36 metric tons).

The ensuing rivalry produced a procession of spectacular achievements and heroes. In 1961 Soviet cosmonaut Yuri Gagarin, only 27, became the first human in space, circling the Earth once and parachuting home to a soft landing in a plowed field. The next year, former Marine combat pilot John Glenn—later a U.S. senator—became the first American to orbit the Earth.

In 1963 came the first woman in space, Soviet textile worker Valentina Tereshkova. Cosmonaut Alexei Leonov took the first spacewalk in 1965, and in 1966 astronauts Neil Armstrong and Dave Scott performed the first space-docking maneuver.

Urged on by President John F. Kennedy’s 1961 promise to put a man on the moon “before this decade is out,” NASA’s von Braun and the Soviet Union’s Korolev sped through a regimen of increasingly complex test flights and orbital missions that culminated in the construction of two giant moon rockets, the American Saturn V and the Soviet N-1, each capable of lifting many tons into space.

Yet tragedy stalked both programs. On January 27, 1967, a fire triggered by an electrical short circuit broke out inside an Apollo space capsule during a training exercise at Kennedy Space Center, killing astronauts Gus Grissom, Ed White, and Roger Chaffee. The Apollo program stalled as Americans reeled from the space effort’s first loss of human life.

The Soviet Union’s program was already in trouble. Korolev died in 1966, and Soviet lunar efforts languished as the decade drew to a close. The Americans recovered, redesigning the flawed Apollo ship and launching the first manned flight aboard von Braun’s giant Saturn V on December 21, 1968. The Soviets, hoping to stay in the race, launched the N-1 on its second test flight on the evening of July 3, 1969. Several hundred feet above the launchpad a metal part shook loose, and seconds later the fully fueled, six-million-pound (three million kilograms) behemoth fell to Earth, exploding in a giant fireball that destroyed the launch complex and Soviet lunar ambitions. Seventeen days later, on July 20, 1969, the Saturn V delivered Michael Collins, Neil Armstrong, and Buzz Aldrin to the moon. Excitement in the U.S. reached apogee.

Three years later the golden age was over. The U.S., strapped for cash during the Vietnam War, abandoned the moon to build the space shuttle and, more recently, the International Space Station. The Soviets, plagued by money problems and rivalry, turned away from the moon and focused on long-duration spaceflight in orbiting laboratories, first Salyut, then Mir.

Public interest in human spaceflight waned. The political imperative faded with détente and later with the fall of the Soviet Union. But it was probably the relative decline in technological bravura that did the most to kill off the audience. Space travel, perhaps the most visionary of all human endeavors, today derives most of its romance from exploits that ended 35 years ago.

In low Earth orbit, the main attraction of human spaceflight was spacewalks, whose novelty soon wore off. Some of the recent ones, requiring astronauts to juggle tons of Erector set components in constructing the space station, are as difficult as any ever attempted, but the nuances of this arcane skill are lost in the viewing. The painstaking movements that unfold so slowly in the weightlessness of space sap the tension from these events. Spacewalking, 42 years after it was invented, is about as spectator-friendly as croquet.

The torch of novelty passed to the robots. The unmanned missions proved their worth early with probes like the Soviets’ Venera, which in 1975 descended through clouds of sulfuric acid toward the surface of Venus, withstanding temperatures of 900°F (482°C) and pressures equivalent to 90 Earth atmospheres in order to transmit the first images of the surface of another planet. NASA’s Voyager 1, launched in 1977 and still transmitting today from the frontier of interstellar space, sped past Saturn and turned backward on February 14, 1990, for a final snapshot: a first ever family portrait of the solar system from the outside looking in. “After that we shut the cameras off,” recalls Voyager project manager Ed Massey. “There was nothing left to shoot.”

Recent years have brought, among many other triumphs, the rovers Spirit and Opportunity, driving on the surface of Mars since 2004; Cassini, currently touring Saturn and its moons; and Deep Impact, which dropped an 820-pound (372 kilograms) projectile into the path of a comet in 2005, then analyzed the resulting crater and debris plume to determine its composition. Orbiting observatories, beginning with the Hubble Space Telescope, provide a never ending supply of breathtaking images of the cosmos.

Despite its shifting fortunes, manned space exploration still retains a viselike grip on the human imagination. Indeed, although it is impossible for all but VIPs, reporters, and NASA employees to get really close to a space shuttle launch at the Kennedy Space Center, crowds still gather on the banks of the Indian River 11 miles (18 kilometers) away to witness a heart-stopping event that never disappoints—more than seven million pounds (three million kilograms) of thrust in a controlled explosion hurling a 4.5-million-pound (two million kilograms) object into the heavens at 25 times the speed of sound.

But it will take the next few years to tell whether humanity's enduring fascination with space will produce another magnificent adventure like the one that began half a century ago. The new moon-Mars effort has brought a fresh air of bustle, but also a real danger that the whole project could fizzle away in a few years with little to show but dusty blueprints. Without a Cold War space race to stoke the competitive fires, the urgency has waned and the money—all but unlimited during the golden age—is scarce and coming slowly this time around.

According to some reports, the first part—reaching the moon and building a permanent base there—can be done for a relatively modest 217 billion dollars spread over 20 years. Describing the moon-Mars initiative as “a journey, not a race,” President Bush has said it can be funded piecemeal without big hikes in NASA’s annual budget—unlike the crash program that followed Kennedy’s moon promise. During that race (most definitely not a journey) NASA at times commanded nearly 4 percent of the annual U.S. budget. NASA’s 17.3-billion-dollar request for 2008 is about 0.6 percent of the total.

Living on the moon will also require technological leaps never contemplated during the Apollo missions. Astronauts must survive prolonged exposure to lethal radiation and build a lunar encampment—perhaps from empty lunar module fuel tanks—that can withstand temperatures ranging from 240°F (116°C) above zero to 240°F (-151°C) below. They must have space suits that can cope with the abrasive effects of moondust—the microscopic potpourri of jagged glass and rock that nearly froze the joints of Apollo space suits after only three days of moonwalks. The new lunar explorers will have to learn to extract oxygen from the dust to use for rocket fuel, breathable air, and water for drinking and radiation shielding. Mars is a project for the next generation—or the one after that.

NASA calls the new space mission Constellation, and has already ordered construction of new spacecraft—a 1960s-like capsule called Orion, famously described by NASA Administrator Michael D. Griffin in 2005 as “Apollo on steroids.” Boosted by a souped-up version of a solid-fuel shuttle rocket called Ares I, Orion will carry a crew of six to the space station and later a group of four to the moon. NASA is also planning a much larger cargo rocket called Ares V, which will be able to lift as much as 150 tons (136 metric tons) to orbit, including the booster rocket, lander, and other hardware needed for a moon expedition.

The first few Constellation moon trips—to begin perhaps as early as 2018—will be sorties to reconnoiter a projected outpost at the lunar south pole. Longer missions will follow. Astronauts will use the base both to explore the moon and to develop and test survival strategies and technology for the more ambitious Mars missions.

Mike Griffin, a plainspoken rocket scientist with previous experience at NASA, the Defense Department, and in private aerospace industry, is masterminding the moon-Mars effort. He has drastically reordered NASA’s priorities to give the initiative a shot at succeeding. Although he praises the shuttle as a “stunning advance in capability and technology,” he never liked the program. The remaining orbiters—Discovery, Atlantis, and Endeavour—will be retired by the end of 2010, as soon as they finish ferrying components to the space station, nearly two-thirds complete. The shuttle’s departure will not be mourned. “It was something well before its time, filled with the hubris of Apollo,” says space historian John Logsdon. “In the end, the shuttle era will be regarded as an interlude in the development of space exploration capabilities.”

When the shuttle age is over, Griffin would like NASA to abandon low Earth orbit projects so it can focus on the moon. Although Orion will be able to carry supplies and astronauts to and from the space station, Griffin prefers to have private enterprise build a workaday rocket for that job, and has ponied up 500 million dollars to help Space Exploration Technologies, a California company owned by PayPal founder Elon Musk, and Rocketplane-Kistler, of Oklahoma City, develop and deliver the new vehicle.

The possibility that private industry might one day provide off-the-shelf rocketry and spacecraft to whoever wants to buy them was unthinkable during the Cold War space race, when virtually every new step was an ultra-expensive technological leap into the unknown. But “new space” is emerging as a serious industry, marrying the know-how of innovative engineers to the cash and acumen of self-made multimillionaires. Musk, not yet 40, dropped out of graduate school in 1995 to earn the first of two Internet fortunes. Burt Rutan, the flamboyant aerospace engineer with muttonchop sideburns, designed and built SpaceShipOne, then had his astronauts fly it twice in two weeks into suborbital space to win ten million dollars offered by the nonprofit X Prize Foundation to encourage the development of low-cost spaceflight. Rutan’s partner in that venture was Microsoft co-founder Paul Allen. Now Rutan is teamed with Virgin Galactic’s Sir Richard Branson to develop SpaceShipTwo, as a tourist vehicle that would carry six passengers on quick up-and-downs at a starting price of $200,000 a seat.

Besides rockets, new space will also need launchpads and destinations. Earlier this year the state of New Mexico introduced a new sales tax to fund the 200-million-dollar Spaceport America, to be built in the desert near Truth or Consequences. And outside Las Vegas, hotel magnate Robert Bigelow is designing and building inflatable space stations. On the ground they look like large umbrellas waiting to unfold, with soft, but durable, fabric wrapped around a rigid core. In space, the fabric would balloon to form compartments. Instruments, life-support machinery, and supplies are stored in the core. A small, unmanned version dubbed Genesis I opened like a flower 346 miles (557 kilometers) above the Earth in July 2006 and has operated flawlessly ever since. Bigelow successfully launched a second prototype in June of this year and intends to put a three-person module in orbit in 2010 and offer space-training programs for astronauts by 2012. Ultimately he hopes to lease modules for use as hotels, labs, or movie studios. Bigelow, who says he got into real estate to earn enough money to indulge his lifelong fascination with space, is a frequent spokesman for new space and is militantly opposed to publicly funded space travel: “It’s not right for governments to be in direct competition with taxpaying companies,” he says. “It’s almost heresy in capitalism.”

In Russia, however, the state is the one looking to make the space profits. In 2001 the Russian space agency Roskosmos began a tourism program by putting American multimillionaire Dennis Tito in a Soyuz capsule and sending him on a visit to the space station. Software developer Charles Simonyi became the fifth space tourist earlier this year, paying more than 20 million dollars for the trip.

Griffin has a zealot’s belief in human exploration of the solar system and has managed to convey this enthusiasm to a once skeptical Congress, giving the new initiative a powerful bipartisan constituency that may enable it to survive the next presidential election. Just as important, he convinced lawmakers to let the shuttle go, and without the shuttle, Orion must move forward, or the U.S. will no longer have a cutting-edge spaceship of its own—a politically unpalatable alternative for many, especially with China inching forward.

Few westerners have visited China’s Jiuquan Launch Center in the Gobi desert. But photographs show facilities strikingly similar to those of NASA’s Kennedy Space Center. Vehicles like those that transport the shuttle carry Chinese rockets to launch after the finishing touches have been added in a smaller version of NASA’s main assembly building. On October 15, 2003, Chinese astronaut Yang Liwei was boosted into orbit from Jiuquan, making China the third nation to put humans into orbit.

Does China’s arrival in orbit herald the start of another space race? “The Chinese and the Americans are a bit like the tortoise and the hare,” says Joan Johnson-Freese, a Chinese space expert with the Naval War College. “The Chinese plod along, launching every few years. The Americans sprint, but haven’t been consistent.” China is methodically acquiring the same skills the Soviets and Americans built during their space race. Two Chinese astronauts made a second flight in October 2005. A third flight in 2008 is expected to carry three crewmen. Tang Xianming, a director of China’s Piloted Space Program Office, says his country wants a space station of its own and is eyeing the moon.

Griffin is not at all unwilling to play up the possibility of a rivalry. Competition fueled the golden age of space, and could end up doing so again. “Will my language be passed down over the generations to future lunar colonies?” he asked in a 2006 speech to the International Astronautical Congress. “Or will another bolder or more persistent culture surpass our efforts and put their own stamp on the predominant lunar society of the far future?”

Others question whether the prize would be worth the cost. They say the return to human space exploration shortchanges the future of unmanned missions just to pay for a quixotic and expensive Apollo rehash. Besides the revelations and sheer wonder delivered by space probes, telescopes, and other instruments, unmanned missions have also produced transformational benefits to humanity in Earth observation, weather forecasting, navigation, and telecommunications. And robots don’t need space suits, radiation shields, toilets, exercise bikes, a bail-out system during launch, or any consumables to speak of except energy.

There’s no argument when it comes to costs: Cassini, NASA’s glittery high-end robotic mission to Saturn, cost the U.S. 3.4 billion dollars, but has been studying the ringed planet and its moons since 2004 and will likely produce pathbreaking science for at least another decade. Deep Impact cost 333 million dollars, and the spacecraft that delivered the projectile is headed for a new mission, probably a rendezvous with a comet. By contrast, shuttle flights, which last around two weeks, cost about a billion dollars apiece in 2002, the last year before the Columbia tragedy, and costs have soared since then.

Griffin’s decision to redirect NASA’s budget toward human space travel has already curtailed planned funding growth for space science and Earth science. NASA’s science budget is projected to remain virtually the same—about 5.5 billion dollars a year—through 2011, while funding for the moon-Mars initiative more than doubles to 8.7 billion dollars. A mission to look for water ice on Jupiter’s moons and two missions to detect Earthlike planets around other stars have been canceled or put on indefinite hold, while budgets for in-house research and analysis, individual research projects, and future low-budget space missions have all been cut.

In January, the Pasadena, California-based Planetary Society, an influential advocacy group, gathered 5,000 signatures for a petition to President Bush protesting these cuts and urging him to “salvage” the “proud history of innovation and exploration in space—before it’s too late.”

Why bother with human spaceflight, when robots do such a good job and do it so much more cheaply? Proponents of human spaceflight argue that only humans have the supple physical coordination and mental agility to get the most from an expedition. But the most compelling argument for human spaceflight may remain the one that worked at the beginning. Space exploration is ultimately about human dreams.

The United States owned the Louisiana Purchase as soon as Thomas Jefferson bought it from the French, but the first thing he did was send Lewis and Clark to walk the property. It isn’t really yours until you’ve been there, say advocates of human space exploration. “I do not see any need at all to justify human spaceflight on the grounds of what it’s going to do for science. It will do a lot for science, but that’s an ‘oh, by the way,’” Griffin says. “The drive to extend our reach—human destiny—is reason enough to go.”

Guy Gugliotta covered space and science for the Washington Post for several years and is co-author with Jeff Leen of Kings of Cocaine, about the Medellin drug cartel.